1. Field of the Invention
The present invention relates generally to a method for detecting the relative orientation of a scanner on a grid pattern, and more particularly to a method for establishing a coordinate system in the memory of a computer which corresponds to the grid pattern through communication with a scanner comprised of two position sensors and a detector array.
2. Brief Description of the Prior Art
Position sensors or cursor control devices which determine the relative position of a point on a grid and thereby determine the movement of a cursor on a visual display system, such as a computer screen, are known in the art. One such device is an electro-optical or electro-mechanical position sensor, commonly called a mouse. As used herein, the term "mouse," or its plural "mice," is used to describe any type of mechanical or optical device capable of detecting its relative motion and/or position over a surface and producing an output signal that can be used to determine the position of a cursor on a computer screen or an address in a computer's memory.
In the typical application, a single electro-optical or electro-mechanical mouse is used in combination with a computer terminal and a software program which allows the operator to enter instructions for a computer without need of a keyboard. Some prior art devices have combined a single mouse with a detector array, capable of detecting pixel data from a scanned surface to produce a type of scanning device. These types of scanning devices have typically been used to scan a single line of text at a time or other indicia located at some position on the scanned page. However, the usefulness of such scanners is limited because the mouse used in the scanner can only detect motion in one dimension and cannot relate its position on the scanned page to a cursor position.
Another type of prior art scanner, such as the "SkySCAN" Model SCN-101 Scanner by Skyworld Technology, Ltd. of Hong Kong, has been utilized to scan a three-to-four inch wide path of information from a scanned page. However, such scanners are limited because they are also constrained to detecting motion in only one dimension, and the recreated images produced by such scanner cannot be combined to form single screens of information, thereby making it impossible to reproduce a standard page of text.
A scanner utilizing two of the above described mice with a detector array is shown in U.S. application Ser. No. 889,130, filed July 23, 1986, which discloses an optical scanner for copying characters on a page and transferring them to the display screen or memory of a computer. Between the scanner and the page is a transparency containing indicia of position, or a grid pattern. The scanner is equipped with an array of photo-sensitive elements for detecting light reflected from the printed characters on the page, but not the transparency. In contrast, the scanner is equipped with two optical mice, which are sensitive to light reflected from the transparency and not the page, for determining the position and relative angle of the detector array with respect to the grid pattern.
Each mouse operates as a counter, detecting the number of vertical or horizontal lines crossed on the grid pattern, to determine the position of each mouse with respect to the grid pattern. Even though the mice may be able to count the number of lines crossed, it is not possible to determine the position of a mouse until a starting point from which to count has been determined and the lines which are being crossed have been designated as vertical or horizontal lines. Thus, mice are typically unable to determine their position with respect to the grid pattern unless they are first oriented (the process of determining the horizontal and vertical axis of a coordinate system which will correspond to the memory addresses of the computer) and initialized (the process of establishing a starting point from which to start counting lines).
A second type of dual mouse scanner is described in Ichinokawa et al, U.S. Pat. No. 4,581,761, issued Apr. 8, 1986, which shows an image scanner which is randomly movable over the surface of a sheet of paper, which is in turn laying over a pad having magnetostrictive properties. The pad is operative to be subjected to pulses introduced at two adjacent ends of the pad (one end representing the vertical axis and the other end representing the horizontal axis) which cause the magnetostrictive material of the pad to produce wave like disturbances in the surface of the pad which travel in vertical and horizontal directions. The position sensors have the ability to detect the raised portion of the pad when a wave passes thereunder and the ability to determine the position of each sensor with respect to the pad by extrapolating the amount of time required for a wave to reach a position sensor from its starting point. Mice capable of determining their own position with respect to the grid or pad do not need to be oriented or initialized.